1. Field of the Invention
The present invention relates generally to data backup. More particularly, the present invention relates to a method and apparatus for managing image data on a sequential storage device.
2. Description of the Related Art
Computer systems and their components are subject to various failures that may result in the loss of data. For example, a storage device used in or by the computer system may experience a failure (e.g., mechanical, electrical, magnetic, etc.) that may make any data stored on the device unreadable. To mitigate the risk of losing data, a computer system may include backup software for making backup copies of data stored on various storage devices.
Some types of backup involve two stages: First, an image of data stored on one or more target storage devices is captured and backed up to disk storage (e.g., one or more hard disk drives). Typically, the data image is an exact copy of the data as stored on the target storage device(s). Second, the data image is copied to sequential storage for archival purposes, such as tape-based storage (e.g., one or more tape drives). As is known, data in disk storage can be accessed randomly, whereas data in sequential storage is accessed serially.
For backup systems, it is desirable to: (1) achieve efficient full image recovery; and (2) achieve efficient restoration of individual files of the image data, referred to as “granular restore”. In granular restore from sequential storage, a file can be restored (recovered from the backed up data image) without having to restore the entire data image on disk. In prevailing backup systems, a data image backed up to disk storage is streamed in its original format to sequential storage. As is known, however, the blocks making up a file may be physically scattered on the disk storage (referred to as “fragmentation”). Hence, if a data image is streamed in its original format to sequential storage, some or all of the files will remain fragmented in the sequential storage. In order to perform granular restoration of a particular file that is fragmented, the sequential storage must be scanned in order to locate all of the blocks of the particular file. In worst case scenario, two blocks of a file being granularly restored may be located at opposite ends of the image in the sequential storage, requiring the entire sequential storage to be scanned. Thus, granular restoration of files from a data image backed up to sequential storage may be an inefficient process.
Accordingly, there exists a need in the art for a method and apparatus for efficient management of image data on a sequential storage device.